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Solidification of heavy castings

100%

Zadera A. , Senberger J. , Pluhacek J. , Carbol Z.

2011

tom Vol. 11, iss. 1

109-112

Quality of the casting material is influenced by great numbers of material properties, metallurgical treatment, and particular solidification conditions too. In the case of solidification of heavy castings the properties and quality of the casting material are considerably changed in consequence of running segregation phenomena, worsen metal feeding conditions, and microporosity formation etc. It can even result in defaulting the required strengths and plasticity of the casting material. The work deals with changes of chemical composition and changes of mechanical properties in places with a long solidification time corresponding to them.

Checking the metallurgy with the aid of inclusion analysis

100%

Senberger J. , Zadera A. , Cech J.

2011

tom Vol. 11, iss. 1

118-122

Results of studying the influence of inclusion morphology on properties of heavy casting are given. The inclusion morphology is dependent on content and kind of the deoxidizing element. Due to segregations the inclusions can be formed in heavy castings under different conditions (by concentration of deoxidizing elements) than in castings of common size. In heavy casting during deoxidation the inclusions of the IVth type occur more frequently. Deoxidation with zirconium shows to be for some heavy casting unsuitable one. Similarly in castings deoxidized with cerium and lanthanum the inclusions of greater sizes occur that can unfavourably influence the steel properties and increase the tendency to crack formation. The inclusion morphology after deoxidation with magnesium is also unsuitable for heavy castings.

Influence of compound deoxidation of steel with Al, Zr, rare earth metals, and Ti on properties of heavy castings

100%

Senberger J. , Cech J. , Zadera A.

tom Vol. 12, iss. 1

99-104

Heavy steel castings deoxidized with aluminium are sometimes brittle intercrystalline failed during their service along primary grain boundaries what is initiated by aluminium nitrides and so called conchoidal fractures are formed. The tendency to forming the conchoidal fractures depends in particular on cooling rate (the casting modulus), aluminium and nitrogen contents in steel. During deoxidation, when manufacturing heavy castings, the elements with high affinity to nitrogen, zirconium or titanium, are added to steel that would decrease nitrogen activity by the bond on stable nitrides. The formation of stable nitrides should reduce the tendency of steel to the formation of conchoidal fractures. Deoxidation was thermodynamically analyzed at presence of the mentioned elements. For particular conditions a probable course of deoxidation was estimated at test castings. The deoxidation course was checked by microanalysis of deoxidation products (inclusions). For service and experimental castings the anticipated composition of inclusions was compared. It has been proved that in heavy castings with high aluminium contents in steel under studied conditions neither the addition of zirconium nor of titanium nor of rare earth metals will prevent the formation of conchoidal fractures.

Increase of liquid metal utilization during production of bearing circle castings for cement furnaces

67%

Zadera A. , Senberger J. , Carbol Z. , Pluhaček J.

tom Vol. 12, iss. 2

111-116

In manufacture of super heavy castings for cement furnaces a saving of liquid metal has been achieved by lowering the riser weight. By solidification modelling with the aid of the Niyama criterion a zone in the riser was designated where the occurrence of foundry defects (shrinkage porosity) can be expected. A plate of the material of dimensions ca 700*800*250 mm was taken from the riser. After thermal treatment the samples for making the bars for the static tensile test were taken from it. Based on done tests it has been found out that mechanical characteristics obtained from the static tensile test correlate, besides contraction, in the chosen level of statistical importance of p = 0.01 with carbon content. Neither in the zone of probable occurrence of defects designated by the Niyama criterion during solidification modelling the drop of strength characteristics was observed. Carbon content in a decisive extent influenced the strength characteristics. In case of ductility and contraction the convenient correlations with carbon content were observed from the riser height of 200 mm only. In the height of 400 mm there was already considerable variation of values and some values were lower ones than is demanded by standards.

Synergy of practical knowledge of molding sands reclamation in heavy casting foundry of iron alloys

67%

Ignaszak Z. , Prunier J. B.

tom Vol. 13, iss. 3

30--36

The paper summarizes research realized by the author in laboratory and industrial conditions (foundries of cast steel and cast iron, castings up to 50 tons) on the effects of the chemically hardened molding sands regeneration using hard/soft rubbing in the dry reclamation. A reference was simultaneously made to advisability of application of the thermal regeneration in conditions, where chromite amount in the circulating (reclaimed) molding sand goes as high as above ten percent. An advisability of connecting standard and specialized methods of examination of the reclaimed sands and molding sands made using it was pointed out. A way of application of studies with the Hot Distortion Plus® method modified by the author for validation of modeling of the thermo-dynamic phenomena in the mold was shown.